两个表的唯一约束

Question

I have two tables:
Country : has ID, Name
State : has ID, Name, CountryID

I defined Country.Name as unique.

I also want to define State.Name as unique per country - ie I can't just define it as unique because two countries may have the same state. But for one country, every state is unique.

How can I do this?

Answer 1

尝试为Name和CountryID列定义UNIQUE ，如下所示：

CREATE UNIQUE INDEX uix ON State( Name, CountryID)